docs: def disp(self, modulo=None):  # TODO: rather assign opt['verb_disp'] as default?
          """prints some single-line infos according to `disp_annotation()`,
          if ``iteration_counter % modulo == 0``
  
          """
          if modulo is None:
              modulo = self.opts['verb_disp']
  
          # console display
          if modulo:
              if (self.countiter - 1) % (10 * modulo) < 1:
                  self.disp_annotation()
              if self.countiter > 0 and (self.stop() or self.countiter < 4
                                or self.countiter % modulo < 1):
                  if self.opts['verb_time']:
                      toc = self.elapsed_time()
                      stime = str(int(toc // 60)) + ':' + str(round(toc % 60, 1))
                  else:
                      stime = ''
                  print(' '.join((repr(self.countiter).rjust(5),
                                  repr(self.countevals).rjust(6),
                                  '%.15e' % (min(self.fit.fit)),
                                  '%4.1e' % (self.D.max() / self.D.min()),
                                  '%6.2e' % self.sigma,
                                  '%6.0e' % (self.sigma * min(self.sigma_vec * sqrt(self.dC))),
                                  '%6.0e' % (self.sigma * max(self.sigma_vec * sqrt(self.dC))),
                                  stime)))
                  # if self.countiter < 4:
                  sys.stdout.flush()
          return self